1. Field of the Invention
The present invention relates to a current supply circuit and a bias voltage circuit.
2. Description of the Prior Art
FIG. 1 shows one example of a conventional current supply circuit 102. As shown in FIG. 1, a first transistor 106 has an emitter 108 connected to a power supply terminal ground 124 through a first resistor 110 and a first collector 112 connected to a power supply terminal VCC 104 through a load. By applying a control voltage to a base of first transistor 106, a collector current which is dependent on the control voltage is supplied to a load. The control voltage is created by a combination of a base-to-emitter voltage of a transistor 114 and a voltage caused by a current flowing through a second resistor 118.
In addition, conventional current supply circuit 102 includes a bias voltage circuit. The bias voltage circuit includes a third resistor 122 that is connected to first collector 112 of first transistor 106. The bias voltage circuit generates an output voltage utilizing a voltage drop by third resistor 122 at the connection point between third resistor 122 and first collector 112.
There are various designs of current sources applicable to the circuit of FIG. 1, which have a positive temperature coefficient. In such cases, the output current varies corresponding to the temperature coefficient, as shown in FIG. 2. That is, the output current supplied to the load greatly depends upon temperature, as shown in FIG. 2. Furthermore, the output current has a temperature characteristic strongly reflecting an effect of a first term of the temperature coefficient, which increases the value of current supplied to the load as temperature rises.
Also, the bias voltage from such a current has a high temperature dependency which causes difficulty in control because the output current is determined by the collector current.